Electrical transformer apparatus

ABSTRACT

Electrical transformer apparatus particularly well suited for use in resistance welding equipment and employing two movable welding electrodes which together with the work piece form a single loop secondary winding in a magnetic transformer. The electrodes are translated longitudinally with respect to the transformer and with respect to each other by means of a fluid operated ram.

United States Patent Humblot [54] ELECTRICAL TRANSFORMER APPARATUS 1 May 16, 1972 [56] References Cited UNITED STATES PATENTS 2,929,915 3/1960 Taylor et al ..2 19/87 Primary ExaminerJ. V. Truhe Assistant ExaminerL. A. Schutzman Attorney-I ishman and Van Kirk Electrical transformer apparatus particularly well suited for use in resistance welding equipment and employing two movable welding electrodes which together with the work piece form a single loop secondary winding in a magnetic transformer. The electrodes are translated longitudinally with respect to the transformer and with respect to each other by means of a fluid operated ram.

ABSTRACT 11 Claims, 4 Drawing Figures Pahia-nted May 16, 1972 2 Sheets-Sheet 1 Patented May 16, 1972 3,663,790

2 Sheets-Sheet 2 1 ELECTRICAL TRANSFORMER APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electric transformer apparatus having magnetically coupled primary and secondary winding, the secondary winding being adapted to be connected to welding electrodes.

2. Description of the Prior Art While not limited thereto in its utility, the transformer apparatus of the present invention is particularly well suited for use in resistance welding equipment. In conventional welding machines employing primary and secondary circuits, the connection between the secondary winding of the transformer and the welding electrodes is provided by a circuit external to the transformer and includes conductors of heavy cross-section which, according to their shape, length, specific resistance and other factors, increase the total impedance of the secondary circuit. To enable the welding electrodes to be moved from point to point as required, the interconnecting conductors by which the electrodes are energized must be capable of moving freely with the welding electrodes.

The electrodes are usually connected to the conductors by a flexible, stranded conductor. The stranded conductors are exposed to considerable fatigue since they are made of copper and subject to considerable electrodynamic reactions. The intrinsic impedance of the stranded conductors increases over a period of time so that the .total impedance of the secondary circuit is increased. The deterioration of the stranded conductors is increased by the amount and frequency with which the stranded conductors are mechanically stressed.

The power of the welding transformer, which may be defined as a function of the electrical power required for weld- 'ing the materials in question, has to meet other conditions as well. Since the impedance of the external secondary circuit of the transformer is quite an important factor, the power of the transformer must be selected with ample margins. The impedance of the external secondary circuit often must be as much as or 6 times the impedance of the secondary winding itself. Since transformers are in most cases manufactured in large numbers, a selection is made over the course of years defining a standardized power range for usual industrial applications. These transformers are often bulky, owing to their high power, and are designed to feed high-impedance external circuits.

In the well known multi-spot welding machines, the principal object is to weld the maximum number of points in one single pass. In the special case of multi-point machines, therefore, a number of additional difficulties are encountered. In particular, the high concentration of welding points to be formed make it necessary to install transformers at a distance from the electrodes. Insurmountable difficulties occur in the task of insuring equal secondary impedances in different transformers fed simultaneously from the same source of current. The result is that secondary currents in certain transformers are inadequate for given welding operations. Increasing the length of the secondary circuits having lower impedance in order to equalize impedances in all secondaries is only a temporary remedy.

SUMMARY OF THE INVENTION According to the present invention, a transfonner device particularly well suited for use in resistance-type electric weld ing units is disclosed. The primary winding of the transformer is connected to an alternating power source. Welding electrodes may be rigidly connected to the respective ends of two parallel support rods which are electrically interconnected at the ends opposite the welding electrodes; the support rods defining in part the transformer secondary winding. The support rods are mounted directly in the magnetic circuit of the power transformer so that the portion of a work piece to be welded between the two electrodes completes the secondary circuit through the transformer. The support rods are movable with respect to the primary winding of a transformer and also with respect to each other.

The special construction of a welding unit employing the transformer of the present invention provides a number of advantages. The secondary winding is placed in direct contact with the material to be welded and is reduced to its simplest form including the portions of the support rods which are situated outside of the magnetic circuit of the transformer and the limited portion of the work piece. The external secondary circuit has an impedance which remains practically constant. Owing to the reduction in the dimensions of the external secondary circuit, the transformer can be designed for a far lower power output and to more moderate dimensions at a specific powering rating than conventional machines. It follows that a considerable reduction in current can be obtained. The circuits in feed apparatus for the welding units can be reduced in size and, correspondingly, cost. If the welding units are employed in multi-spot machines, the reduced size of the transformer enables a large number of units to be installed in one machine without increasing the space occupied by the equipment. As a result, the cost of each welding operation is reduced.

In one embodiment of the invention, a fluid operated ram is connected with each support rod for translating the rods with respect to the frame.

A large number of units can be installed side-by-side and the machines can be adapted to special functions without tedious prior planning to equalize the impedance of the various secondary circuits. Furthermore, the units. can be assembled, dismantled and maintained rapidly and conveniently.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention with its numerous objects and advantages will be better understood by reference to the follow ing drawings which show one embodiment of the present invention wherein like elements bear like reference numerals throughout the several figures.

FIG. I is a partial cross-sectional view in perspective showing the present invention in the environment of a novel welding unit.

FIG. 2 is a perspective view of the welding unit of FIG. 1 as viewed from the electrode end.

FIG. 3 is a cross'sectional view of the along the line III-III in FIG. 1.

FIG. 4 is also a cross-sectional view of the viewed along the line IV-IV in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I In the environment of a novel welding unit, as shown in FIG. 1, the present invention includes two welding electrodes 1, 2 supported by means of sockets 3, 4 from the lower ends of two welding unit as seen welding unit as vertical support rods 5, 6 respectively. The support rods 5, 6

are mounted in a frame structure reference numeral 8.

The frame structure 8 at its central portion has a laminated magnetic transformer circuit 11 composed of a stack of plates secured between a lower frame member 12 and an upper frame member 13 by means of connecting rods 14. The upper frame member 13 includes a cap 16. A stud 17 is secured to the cap 16 and offers a means by which the welding unit can be mounted to a suitable machine support.

The plates constituting the magnetic circuit 11 of the transformer have a substantially rectangular configuration as seen more clearly in FIG. 3. Each plate 21 has two lateral branches 22 and a central branch 23. The width of the central branch 23 is twice that of the two lateral branches 22. Two plates of the same layer are juxtaposed along a central joint line 25. The plates are combined in small groups and separated from one another by insulating plates 26 seen in FIGS. 1 and 2. The groups of plates at the end of the magnetic circuit 11 are separated from the frame members 12 and 13 by means of two insulating plates 28 and 29 respectively.

generally designated by the Around the middle branches 23 of the plates forming the magnetic circuit 11 are two primary winding transformer coils 32, 33. According to the particular welding functions in mind, either one or both of the coils 32, 33 can be fed from a suitable A.C. source.

The secondary circuit of the transformer is a single turn formed by the conductive support rods 5, 6, a shunt 36 interconnecting the upper ends of the support rods and, of course, the portion of the work piece between the two welding electrodes l and 2.

in the embodiment shown, the shunt 36 consists of a stack of U-shaped flexible copper laminates secured at their ends by means of bolts 38, 39 to plates 41, 42 integrally joined to the upper ends of support rods 6 respectively.

The two electrode support rods 5 and 6 are mounted to slide in the longitudinal direction in lower guide 45 and upper guide 46. The lower and upper guides are made of an insulating material and are mounted flush in the lower frame member 12 and the upper frame member 13 respectively.

The sliding movement of the two support rods 5 and 6 is brought about by the two double-acting rams 47, 48 (FIG. 2) which are supplied with fluid under pressure, for example compressed air. One of the elements of the double-acting rams, such as the cylinder, is rigidly secured to the frame 8 while the piston is rigidly secured to the corresponding support rod, 5 or 6. In the embodiment shown, each of the two rams 47 and 48 contains a stud 51 extending from the cylinder and affixed to the frame 13 by a nut 52. The piston 54 is secured to a piston rod 55, the outer end of which carries a driving plate 57 through which the corresponding support rod 5 or 6 passes as seen more clearly in FIG. 2. The drive plate 57 is rigidly secured to its respective support rod by means of a set screw 58 which clamps the bifurcated section of the sup port plate 57 against the support rod. The bifurcated section of the drive plate 57 is formed by a split 59 and allows the set screw 58 to secure the support rod tightly within the plate 57.

The two conductive support rods 5 and 6 are cooled by the circulation of a fluid, such as water. For this purpose the rods are of a tubular construction. The lower ends of the support rods are closed by the sockets 3 and 4 and the electrodes 1 and 2 respectively (FIG. 1). The upper ends of the support rods are equipped with sockets 62 and 63 which support tubes 64 and 65 respectively (FIGS. 1, 3 and 4). The tubes 64 and 65 extend coaxially inside their respective support rods to the lower end of the rods in the vicinity of electrodes 1 and 2 which seal the rods.

The socket 62, as seen in FIG. 1, is connected by a bellows type structure 66 to an orifice 67. The orifice 67 is provided in the cap 16 and can be connected to a cooling-water supply source. The upper part of the annular space between tube 64 and the inner wall of support rod 5 is connected by a flexible tube 68 to the upper sockets 63 of support rod 6. In a similar fashion, the upper part of rod 6 also contains an annular space between the tube 65 and the inner wall of the rod 6 and a similar bellows-type structure (not shown) is connected from the annular space at the top of rod 6 to an orifice 71 (FIG. 4) in the cap 16 for evacuation of the cooling fluid. The temperature of fluid exhausting through the orifice 71 will be increased in the course of passage through the welding unit.

The operation of the welding unit is described below. The work pieces to be welded are placed beneath the electrodes 1 and 2 and rest on counter-electrodes (not shown). The welding cycle commences by supplying compressed air to the two rams 47 and 48 which cause the two support rods 5 and 6 to descend. Thus the secondary circuit of the transformer is closed. The above steps are known as the approach phase. The electrodes are then applied under pressure to the work pieces to be welded. Voltage is applied to the primary of the transformer for a certain preselected period. This is known as the welding phase. Similarly, the electrodes are held tightly against the work pieces for a selected period of time to produce the forging phase. Finally, the pressure in the doubleacting pneumatic rams 47, 48 is reversed and the electrodes are released from the welded work pieces.

The individual control of the respective support rods enables a very even pressure to be applied to all of the various welding points of the work pieces.

The numerous advantages offered by the welding unit described above will be obvious to one skilled in the art. While the novel transformer assembly has been described in one particular embodiment, it will be understood that various modifications and substitutions can be made without departing from the spirit of the invention. Accordingly, the present invention has been described by way of illustration rather than limitation.

What is claimed is:

1. In an electric welding unit of the type wherein a current path through a current transformer secondary winding is completed through a portion of a workpiece situated between a pair of work contacting electrodes, the improvement comprising:

a structural frame;

transformer means mounted in the frame and having a primary winding for receiving electrical power and means movable with respect to the primary winding and defining a secondary winding, said movable secondary winding defining means including a pair of electrically conductive electrode support rods mounted in the frame and magnetically coupled to the primary winding, said support rods projecting from the frame at one side and being individually movable with respect to the frame; and

two welding electrode means, each of said electrode means including a welding electrode and being connected respectively to the projecting end of one of the two electrode support rods whereby current induced in said support rods is supplied directly to said electrode means.

2. The electric welding unit of claim 1 wherein:

the transformer has magnetic coupling members positioned between the primary and secondary windings; and

the magnetic coupling members are a portion of the structural frame.

3. The electric welding unit of claim 1 further including:

actuating means connected to the structural frame and the respective electrode support rods for moving the support rods with respect to the frame.

4. The electric welding unit of claim 3 wherein:

the electrode support rods are individually movable with respect to the frame along the longitudinal axes of the respective support rods; and

the actuating means is a pair of fluid rams connected respectively between the frame and the support rods.

5. The electric welding unit of claim 4 wherein:

the pair of fluid rams are a pair of piston and cylinder assemblies, the cylinders being connected to the structural frame with the cylinder axes parallel to the electrode support rods and the pistons being connected respectively to the support rods.

6. The electric welding unit of claim 3 wherein:

the structural frame includes a first end member through which the support rods project at the one side of the frame and a second end member disposed at the generally opposite side of the frame; and

the transformer has a plurality of magnetic coupling members sandwiched between the first and second end members.

7. The electric welding unit of claim 6 wherein:

the two parallel electrode support rods are electrically insulated from the plurality of magnetic coupling members and extend through the plurality of magnetic coupling members.

8. The electric welding unit of claim 1 wherein:

the electrode support rods are hollow rods.

9. The electric welding unit of claim 8 wherein:

the electrode support rods have liquid cooling means for cooling the welding electrodes at the projecting ends of the support rods.

7 10. The electric welding unit of claim 9 wherein:

the cooling means includes a cooling tube extending coaxially within each of the hollow support rods, a fluid conduit interconnecting the hollow support rods at the ends opposite the projecting ends of the rods, and at least one flexible tube connected between the structural frame and one of the cooling tubes within the support rods. 

1. In an electric welding unit of the type wherein a current path through a current transformer secondary winding is completed through a portion of a workpiece situated between a pair of work contacting electrodes, the improvement comprising: a structural frame; transformer means mounted in the frame and having a primary winding for receiving electrical power and means movable with respect to the primary winding and defining a secondary winding, said movable secondary winding defining means including a pair of electrically conductive electrode support rods mounted in the frame and magnetically coupled to the primary winding, said support rods projecting from the frame at one side and being individually movable with respect to the frame; and two welding electrode means, each of said electrode means including a welding electrode and being connected respectively to the projecting end of one of the two electrode support rods whereby current induced in said support rods is supplied directly to said electrode means.
 2. The electric welding unit of claim 1 wherein: the transformer has magnetic coupling members positioned between the primary and secondary windings; and the magnetic coupling members are a portion of the structural frame.
 3. The electric welding unit of claim 1 further including: actuating means connected to the structural frame and the respective electrode support rods for moving the support rods with respect to the frame.
 4. The electric welding unit of claim 3 wherein: the electrode support rods are individually movable with respect to the frame along the longitudinal axes of the respective support rods; and the actuating means is a pair of fluid rams connected respectively between the frame and the support rods.
 5. The electric welding unit of claim 4 wherein: the pair of fluid rams are a pair of piston and cylinder assemblies, the cylinders being connected to the structural frame with the cylinder axes parallel to the electrode support rods and the pistons being connected respectively to the support rods.
 6. The electric welding unit of claim 3 wherein: the structural frame includes a first end member through which the support rods project at the one side of the frame and a second end member disposed at the generally opposite side of the frame; and the transformer has a plurality of magnetic coupling members sandwiched between the first and second end members.
 7. The electric welding unit of claim 6 wherein: the two parallel electrode support rods are electrically insulated from the plurality of magnetic coupling members and extend through the plurality of magnetic coupling members.
 8. The electric welding unit of claim 1 wherein: the electrode support rods are hollow rods.
 9. The electric welding unit of claim 8 wherein: the electrode support rods have liquid cooling means for cooling the welding electrodes at the projecting ends of the support rods.
 10. The electric welding unit of claim 9 wherein: the cooling means includes a cooling tube extending coaxially within each of the hollow support rods, a fluid conduit interconnecting the hollow support rods at the ends opposite the projecting ends of the rods, and at least one flexible tube connected between the structural frame and one of the cooling tubes within the support rods.
 11. The apparatus of claim 1 wherein said movable secondary winding defining means further comprises: shunt means electrically connecting the ends of said electrode support rods positioned remotely of said welding electrode means. 